The Frontier Justice is an unlockable primary weapon available for the Engineer released with the Engineer Update. This shotgun cannot randomly Crit and has half the magazine size of the regular Shotgun (3 from 6), but can get Revenge Crits: For every kill your Sentry racks up, upon its destruction the Frontier Justice gets 2 guaranteed Crits. For every assist, it gets 1. This applies even if the Engineer destroys his own Sentry with the PDA.

Taunting with the Frontier Justice will make the Engineer pull out his guitar, strum it, and slam it on the ground killing anyone unlucky enough to be infront of him.